1. Field of the Invention
This invention relates to vertical, horizontal, rotational and structural stabilization of mooring turrets for suspension of mooring lines, marine risers and related oil-well lines and equipment from ships for petroleum drilling and production.
2. Relation to Prior Art
Ships structured for petroleum drilling and production in offshore and oceanic bodies of water are seabed-anchored from bottoms of various types of turret cylinders through which drilling and production activities are accomplished. Turret-cylinder changes of direction, position and verticality must be prevented to the fullest extent possible while the largest of ships toss, turn, change directions and change positions frequently as a result of ambient conditions.
Economical construction and physical weight of ship structure can not accommodate sufficiently rigid hulls to prevent resilient distortion of ship-deck turrets and turret bases for suspension of oil-well lines and mooring lines. Stabilization of mooring turrets related to petroleum-exploitation systems on necessarily resilient hulls is critical.
Examples of different but related mooring-turret systems are described in the following patent documents. U.S. Pat. No. 5,339,760, issued to Korsgaard, taught a submersible buoyant mooring element that raised buoyantly into sealing contact with a turret cylinder of a ship, but was silent about structure of the turret cylinder for supporting rotational change and radial displacement. U.S. Pat. No. 5,181,799, issued to Carruba, described a rigidly vertical tube attached to a seabed and supported triangularly at a platform-pivot point by support members that were attached to the seabed at separately distant positions for offshore petroleum activities. U.S. Pat. No. 5,025,742, issued to Urdshals, described a turret type of moor on a bow of a seagoing vessel such as an oil tanker without reference to a turret cylinder for petroleum-exploitation. U.S. Pat. No. 4,943,188, issued to Peppel, taught a rotative lug-anchor connector for releasable securement of a tether from a tension-leg platform to a seabed but did not describe working relationship to or structure of a turret cylinder for a marine vessel. Japanese Patent Number 61-155086, issued to Ishida, described a roller-supported turret with equal distribution of weight and rotative drive on a plurality of rollers that would require economically prohibitive weight and cost for vessel construction and for turret construction and operation. Finally, U.S. Pat. No. 4,753,553, issued to Carlsen et al, taught turret structure and turret-bearing structure which accommodated structurally resilient distortion of a marine hull and of a turret base, but not with universal stabilization as taught by this invention.
The Carlsen patent described a mooring turret having a turret-cylinder (skirt 13) axis with maximized concentricity to a cylinder wall 23 extending vertically through a hull 14. A plurality of axial or vertical bearing structures 30 in combination with a plurality of radial or horizontal bearing structures 46 were pressure actuated to compensate for resilient distortions of the hull 14 and of bearing races 25 and 37 that result from marine and weather effects on the hull 14 and on the races 25 and 37 respectively. This facilitated reduction of weight and size of the mooring turret or rig 11 having a platform 12 from which the skirt 13 was extended downward vertically through the cylinder wall 23 which had emergency bearing members 22, 22a and 22b in sliding contact with the cylinder wall 23. Concentricity of the skirt 13 with the cylinder wall 23 and parallelism of the platform 12 with a deck of the hull 14 created instead of solving yet a greater problem. It prevented universal stabilization. Instead, it caused the rig 11 to sway, tip, yaw, heave and turn with unstable positioning of the hull 14 in response to waves, water current and weather. In addition, bearing positioning and control were inadequate for minimizing weight and size of the turret. Further problems included interference of mooring lines, choke/kill lines and other equipment with risers in a moon pool.